A jacket used for a floppy disk is generally in the form of a bag formed of a sheet of high molecular resin such as vinyl chloride resin and ABS resin, and a liner formed of a fiber sheet is bonded to the inside thereof. The said liner formed of a fiber sheet is provided mainly for the purpose of interrupting the direct contact of the floppy disk with the resin sheet constituting the jacket proper, thereby to avoid the abrasion or damage of the floppy disk surface, and of cleaning the surface of the floppy disk. A variety of fiber sheets have already been proposed for such purposes. For example, Japanese Patent Application Kokai (Laid-open) No. 58-7705 (1983) discloses a nonwoven fabric formed of polyester fiber. Japanese Patent Application Kokai (Laid-open) No. 54-49115 (1979) discloses a nonwoven fabric formed of polypropylene fiber. Japanese Utility Model Application Kokai (Laid-open) No. 57-71280 (1982) discloses a nonwoven fabric formed of regenerated cellulose fiber. The methods used in these disclosures to stabilize the form of the nonwoven fabric involves melt-bonding the fibers to one another or adhesion-bonding the fibers to one another with an adhesive agent.